What happened: As part of a grand jury investigation that's still secret, the Justice Department asked a federal magistrate judge to approve monitoring of an unnamed person's e-mail correspondents.

The request had a twist: Instead of asking to eavesdrop on the contents of the e-mail messages, which would require some evidence of wrongdoing, prosecutors instead requested the identities of the correspondents. Also included in the request was header information like date and time and Internet address--but not subject lines.

The federal magistrate judge balked and asked the Justice Department to submit an additional brief to demonstrate that such a request would be legal.

Instead, prosecutors asked Judge Hogan to step in. He reviewed the portion of federal law dealing with "pen register" and "trap and trace" devices--terms originating in the world of telephone wiretapping--and concluded it "unambiguously" authorizes the e-mail surveillance request.

Though the language may be clumsy, Hogan said, the Patriot Act's amendments authorize that type of easily obtainable surveillance of e-mail. All that's required, he said, is that prosecutors claim the surveillance could conceivably be "relevant" to an investigation.

Excerpt from the court's opinion:
"In 2001, Congress enacted the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001 (the "USA Patriot Act"), Section 216 of which explicitly amended the authorities relating to pen registers and trap and trace devices...by expanding the definitions of these devices to include "processes" to obtain information about "electronic communication."

"Commenting on the very language that was finally enacted in Section 216 of the USA Patriot Act, several members of Congress highlighted the fact that the amendments would bring the state of the law in line with current technology by making pen registers and trap and trace devices applicable to the Internet and--more to the point--e-mail.

"For example, a section-by-section analysis of the bill that Representative John Conyers included in the record before the final House vote, which contains the same language that was finally enacted by Congress, states that Section 216 "extends the pen/trap provisions so they apply not just to telephone communications but also to Internet traffic."

"In addition, Senator Jon Kyl, who is currently Chairman of the United States Senate Judiciary Subcommittee on Terrorism, Technology & Homeland Security, noted that the same language in the Senate version of the bill "would codify current case law that holds that pen/trap orders apply to modern communication technologies such as e-mail and the Internet, in addition to traditional phone lines."

"The Congressional Research Service also published a legal analysis of the USA Patriot Act that states that the Act "permits pen register and trap and trace orders for electronic communications (e.g., e-mail)."

"The plain language of the statute makes clear that pen registers and trap and trace devices may be processes used to obtain information about e-mail communications. The statute's history confirms this interpretation and there is no support for a contrary result."

About the author

Declan McCullagh is the chief political correspondent for CNET. You can e-mail him or follow him on Twitter as declanm. Declan previously was a reporter for Time and the Washington bureau chief for Wired and wrote the Taking Liberties section and Other People's Money column for CBS News' Web site.
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